1. Field of the Invention
The present invention relates to a burner for premix combustion of liquid and gaseous fuels.
2. Discussion of Background
In burners for premix combustion of liquid and/or gaseous fuels, the migration of the flame into the burner, also called flashback of the flame, constitutes a major problem. In addition, the aerodynamics in the case of these burners have to be designed in such a way that local zones which have a long retention time and in which the fuel/air mixture may ignite (=self-ignition) are avoided. If a swirl flow is generated in such a way that high peripheral velocities occur in the vicinity of the axis, for example when radial swirl registers are used, the axial velocity in the center is low. Since high degrees of turbulence occur at the same time, the flame may spread out against the direction of flow and it then migrates into the burner, as a result of which overheating problems generally occur. In practice, this leads to restrictions in the choice of swirl generation. The generation of a swirl-flow field requires the flow to be enclosed in a space, the best space being rotationally symmetrical. The outer limit of this space causes a flow boundary layer which always has the condition of disappearing velocity at the wall. The same applies to fuel lances fitted in the center. The portion of the mixture which flows directly along the wall will be retained for an undesirably long time in the burner. Especially low velocities occur at the outer limit of the swirl-flow field, since, at constant total pressure in the arrangement, the static pressure increases from inside to outside, whereby the dynamic pressure, which is represented by the absolute velocity, becomes lower and lower with increasing radius. These low velocities may possibly no longer prevent the flame from being propagated from the combustion space along the boundary layer into the burner and from then overheating and destroying the latter.
U.S. Pat. No. 4,932,861 to Keller et al. has disclosed a burner which represents under premix conditions for liquid and/or gaseous fuels the solution which has become best known up to now in this field in order to be able to remove the abovementioned shortcomings without the implementation of additional features.
However, development in gas-turbine construction is aimed at substantially increasing the compressor pressure ratios, so that the reliability of the abovementioned burner is automatically reduced for the said reasons.